Recently, for example, a liquid crystal display device has been widely used in liquid crystal televisions, monitors and mobile phones as a flat panel display having features such as being thinner and lighter in comparison to a conventional cathode ray tube. Such a liquid crystal display device includes a backlight device that emits light and a liquid crystal panel that displays a desired image by acting as a shutter against light from a light source provided in the backlight device.
Furthermore, as the aforementioned backlight device, an edge light type or a direct type backlight device is provided in which a linear light source constituted of a cold-cathode tube or a hot-cathode tube is disposed on a side of or below the liquid crystal panel. However, the cold-cathode tube such as described above and the like contain mercury, resulting in difficulty in, for example, recycling the cold-cathode tube to be disposed of. In view of this, a backlight device whose light source is light emitting diodes (LEDs) in which mercury is not used has been developed and practically used.
Additionally, in the conventional backlight device such as described above, white light is obtained usually by using a white LED or by being provided with three colors of LEDs that emit red (R), green (G) and blue (B) light and mixing these three colors of light, and the device emits the white light toward the liquid crystal panel as illumination light.
However, in the LED such as described above, in general, the luminous efficiency declines as the ambient temperature rises. Consequently, the balance between the amounts of red, green, and blue light is lost. As a result, luminous quality may decline because white light cannot be obtained appropriately, or luminance irregularity occurs.
In view of this, in conventional backlight devices, there have been proposals, as recited in JP2005-353507A, JP2006-49098A and JP2006-64733A for example, to dissipate heat generated by LEDs to the outside by providing a heat dissipation mechanism using a heat dissipating plate or an elastic sheet having heat conductivity etc. In addition, the conventional backlight device has been considered to be able to prevent a decline in luminous efficiency and a decline in luminous quality by suppressing a rise in the ambient temperature caused by heat from LEDs.